The present invention relates generally to a semiconductor device and a method for manufacturing the same, and more particularly to a semiconductor device capable of preventing a floating body effect in a peripheral region, thereby improving the operation characteristics thereof, and a method for manufacturing the same.
Current design trends in semiconductor devices include increasing the level of integration, increasing operation speed, and reducing power consumption. As the above design trends continue, a semiconductor device using a silicon-on-insulator (SOI) substrate, in place of the typical substrate made of bulk silicon, has been highlighted in the art. A device formed on the SOI substrate provides advantages over a device formed on the substrate made of bulk silicon in that it is possible to accomplish high speed operation through utilization of a small junction capacitance, accomplish voltage reduction through utilization of a low threshold voltage, and accomplish prevention of a latch-up phenomenon through utilization of complete isolation.
A conventional SOI device includes an SOI substrate having a structure in which a buried oxide layer and a silicon layer are sequentially stacked on a silicon substrate, gates which are formed on the silicon layer of the SOI substrate, and junction areas which are formed in the silicon layer on both sides of the gates such that the lower ends of the junction areas come into contact with the buried oxide layer. In the conventional SOI device, the portions of the silicon layer which are placed under the gates, that is, the bodies of transistors, are floated by the presence of the junction areas and the buried oxide layer.
Therefore, since the conventional SOI device has an floating body cell (FBC) structure in which the bodies are floated, charges can be stored in the floated bodies, and therefore, the size of cells can be decreased because it is not necessary to separately form capacitors for storing charges.
However, in the conventional SOI device, which include bodies having the floating structure in both a cell region and in a peripheral region, an undesired floating body effect can be caused in the peripheral region, and due to this, mis-operation of the device is likely to occur. That is, when the floating body effect is caused in the peripheral region, transistors in the peripheral region operate and current flows from drain areas to source areas, charges are stored in the bodies and the voltages of the bodies decrease. Consequently, as electron holes are temporarily discharged to the source areas, mis-operation is likely to occur.
As a result, in the conventional SOI device, due to the fact that the undesired floating body effect may occur in the peripheral region leading to device mis-operation, whereby the operation characteristics of the SOI device may deteriorate.